1. Technical Field
The present invention relates to semiconductor devices, and more particularly, to a semiconductor device of a CMOS structure, which includes a dual-work function metal gate having work functions adjusted by controlling a composition of components such as nitrogen (N), aluminum (Al), and titanium (Ti) within a TiN electrode, and a method of manufacturing the same.
2. Description of the Related Art
In a semiconductor device, a silicon oxide layer (SiO2) is generally used as a gate dielectric layer of memories and logics. However, reduction in design rule of semiconductor devices results in increase in gate leakage current, causing a limit of the silicon oxide layer.
Reduction in tunneling current is obtained by increasing the thickness of the gate dielectric layer and a high permittivity (high-k) dielectric material is suggested as a solution to this. In addition, various studies have been made to minimize depletion of polysilicon through application of metal gate electrodes instead of polysilicon gate electrodes.
To obtain symmetrical and low threshold voltages in formation of a complementary metal-oxide semiconductor (CMOS), a technology using two metals having ideal work functions of an NMOS and a PMOS is suggested, but has a problem of causing etching failure of a metal electrode.
In particular, metals such as Ru, Mo, Pt, and the like, which can be used for an electrode of a PMOS and have high work functions, are not suited to a gate first process due to etching difficulty and low thermal stability. Thus, it is advantageous to use TiN in formation of a CMOS device, since TiN allows easy etching. However, it has been reported that TiN has an insufficient work function to be used for nMOSFETs and pMOSFETs.
Korean Patent Registration No 10-0463239 (Registration Date: Nov. 30, 2004) discloses a method of manufacturing a CMOS device having a dual-metal gate electrode. The dual-metal gate electrode of the CMOS device includes a first metal gate electrode, which is formed on an nMOS region and comprised of a material selected from among Ru1-xTaxNy, WAx (A=Ti, Ta, Nb) and Ru1-xCxOy (C=Ti, Ta), and a second metal gate electrode, which is formed on a pMOS region and selected from among Ru1-xTixNy, WBx (Ni, Mo, Pt) and Ru1-xDxOy (D=Ni, Mo).